Former Health and Human Services Secretary Tommy Thompson, who served four terms as Wisconsin governor, is securing financial pledges and ramping up his outreach to longtime political aides in preparation for a possible campaign against Democratic Sen. Russ Feingold.

Thompson has alerted his Washington-based law firm of his moves and is contacting key clients about the prospect of challenging Feingold, the most tangible signals yet that he’s seriously exploring a 2010 campaign.

“The governor has taken additional steps in the past week and will continue to do so over the next several weeks. If the meetings go well, you can expect to see an exploratory committee set up near the end of March,” former state commerce secretary and Thompson campaign manager Bill McCoshen told POLITICO.

Another longtime Thompson ally said the governor already has $200,000 in potential donations for a campaign that doesn’t yet exist.

“If you talked to me two weeks ago, I would have put it at a 50-50 shot. Now it’s at 70,” said the Thompson aide, who requested anonymity to avoid offending his friend. “He’s asking serious questions like, ‘Who would run the campaign? Who would do the fundraising? When would we announce? How much could we raise?’”

Despite Thompson’s steps, political insiders in both parties in Washington and Wisconsin remain skeptical of Thompson’s commitment to challenging Feingold, a three-term incumbent.

“Gov. Thompson has taken every opportunity in the media to try to remind voters he’s popular and get his ego stroked,” said Sachin Chheda, a Democratic consultant and chairman of the Milwaukee County Democratic Party. “We’re not seeing anything other than the usual dance where he likes to see his name in the paper, which occurs every few years when an election comes up.”

Thompson, who ran for the 2008 GOP presidential nomination, has twice openly contemplated a shot at his old job, most recently in spring 2009. And he’s frequently been mentioned as a possible Senate candidate over the past two decades. Last November, he even joked that he was looking at a mayoral race as a platform for a political comeback.

A Rasmussen Reports survey taken just last week demonstrates why Thompson might be seriously looking at a Senate bid.

For national Republicans, Thompson’s candidacy would be a recruitment coup, a development that would broaden the 2010 electoral map by forcing Democrats to defend a seat that has yet to surface on national radar as a competitive race. And any plausible path to a Senate majority would most likely involve a GOP victory in a Democratic-leaning state such as Wisconsin, where the contest would immediately become competitive with Thompson’s candidacy.

Asked about the possibility of a Senate run in late January, Thompson told POLITICO: “I’m not saying ‘no.’”

“This isn’t something he thought up,” said Thompson spokesman Jason Denby. “This is mostly people coming to him, lots of people in Washington, saying he should do it.”

With the luxury of a July filing deadline, Thompson is in no rush to make up his mind. Allies insist he is more serious about this race than others he’s chewed over but stress that any formal announcement would not come until the state party convention in May.

That leaves a considerable shadow looming over the two lesser-known GOP candidates, who are still working to build name identification and raise enough funds to compete with Feingold.

From an organizational standpoint, GOP leaders, who respect the goodwill that Thompson earned from his historic four-term run as governor, would prefer to avoid a drawn-out parlor game.

“As I talk to the grass-roots, it’s a question that comes up frequently. What about Tommy?” said Eau Claire County Republican Chairman Brian Westrate. “From a chairman’s perspective, if he’s going to do it, the sooner he does it, the better.”

But no party leader — or smart candidate — is ready to publicly criticize the state’s most popular GOP figure of the past two decades for dawdling.

“Terrence has enormous respect for the governor and the decision he has to make with his family,” said Wall campaign spokesman Bob Delaporte.

Still, despite Thompson’s marquee name, national fundraising ability and shiny poll numbers, there are several indicators that suggest a campaign would be more challenging than a first glance might suggest.

There’s Thompson’s wife, Sue Ann, who has made clear the advice she has given her husband about returning to the political arena.

“I always discourage it. You can’t go back, you need to look ahead. My philosophy is quit while you’re ahead,” she told Madison magazine in a March 2010 cover story.

On Feb. 3, Thompson showed another sign of moving beyond politics, enlisting as an adviser to the Peak Ridge Capital Group, whose operations include a hedge fund — a position that would not be an asset in the current campaign environment.

And the millions he made as an adviser to law and health care firms would also provide fodder for Democratic attacks similar to the ones that pilloried Republican Dan Coats after he recently announced his Senate candidacy in Indiana.

Potentially more damaging are Thompson’s comments in October, when he became one of only a handful of prominent Republicans to shower praise on the Democratic health care bill produced by the Senate.

The former Bush administration official even went so far as to issue a joint statement with former House Majority Leader Dick Gephardt praising the Senate Finance Committee’s legislation as “another important step toward achieving the goal of health care reform this year,” adding that “failure to reach an agreement on health reform this year is not an acceptable option.”

His work at the Health and Human Services Department, which included implementing more regulations on smoking and health insurance, might also prove ripe for attack by small-government conservatives who drive turnout in Republican primaries.

“The grass roots are looking for people who stick to their fiscal principles once they’re elected,” Westrate said.

Chheda was less charitable. “The fact that he supported the Senate health care bill in this environment, I don’t know if he’s going to even win a primary. He immediately becomes the left-wing candidate in a three-way primary.”

“I think he’s going to run into a buzz saw, and I think the people around him are smart enough to know that,” he added.

Aides say Thompson is aware of his unique vulnerabilities but learned from his brief 2008 presidential run, in which questions about his business dealings helped keep his campaign from lifting off the ground.

“Is it possible Tommy won’t run? I can’t deny that. But the steps he has taken this time are more thoughtful and more deliberate at any other time in the past 12 years,” said McCoshen, referring to the period of time since Thompson’s last campaign for governor. “Remember, Tommy hasn’t been on the ballot in 12 years in Wisconsin, yet he still has 95 percent name identification.”